Live aquarium plants need light, nutrients, and carbon dioxide to grow. Most planted tanks already contain some CO₂ from fish respiration, bacteria, and natural gas exchange. The problem is that demanding plants may use that supply faster than the aquarium can replace it. Adding CO₂ can improve plant growth, color, and overall health. It can also make carpeting plants and other demanding species much easier to keep. Still, a CO₂ system is not a magic button. Light, fertilizer